This “margins” concept can be interpreted several different ways. Think of your margins as the your technical limitations- how efficiently can you move? how skillful are you? what kinds of movements can you perform well, simply perform, or are unable to perform?
Your physical and mental limits also represent your “margins” as an athlete. What are your performance numbers in the gym? Benchmark workout times? Lifting personal bests? How much are you capable of enduring and pushing through? How much are you willing to make yourself physically suffer in the context of a training session?
When it comes to training at our limits, we must accept that at times we are going to exceed our abilities and fail during a workout. This could be a breakdown in safe technique, muscle failure or exhaustion, or simply a mental unwillingness to continue. Understand that the vast majority of our training needs to be spent safely testing and pushing the limits. This is what we call smart, everyday training, where intensity and volume are dictate by how we feel that day. Then there are times where we need to open up the throttle and scorch a workout for the sake of seeing the true limits of our capacity. Consider these rare moments as opportunities to test your fitness and mental readiness state in real time. Find the margins, push the boundaries our further; rinse, lather, repeat.